Wpływ syntetycznych induktorów odporności nabytej na hamowanie rozwoju szarej pleśni u pelargonii i poinsecji [The effect of synthetic inducers of systemic resistance in inhibiting grey mold development on geranium and poinsettia]

Several chemical activators of resistance were tested to evaluate their efficiency in restricting development caused by Botryotinia fuckeliana (Botrytis cinerea) on geranium and poinsettia leaves. The used signal pathway inducers of salicylic acid, such as DL-â-aminobutyric acid (BABA), g-aminobutyric acid (GABA) and benzothiadiazole (BTH), at the applied rates markedly inhibited the development of grey mould in the both plant species. The mentioned inducers showed no toxic or restricting effect on the fungus growth and development under in vitro conditions. Only methyl jasmonate (Me-JA), a potential activator of independent signal transduction pathway, at the applied quantities (O,1–1,0 mg·ml-1), noticeably enhanced the disease spot development probably through stimulation of ethylene synthesis in plant. Me-JA added to medium with B.cinerea showed a strong antifungal action, whereas ethylene significantly stimulated mycelium growth in the in vitro cultures

Rozwój Botrytis cinerea Pers. ex Fr. na liściach wilczomlecza pięknego (Euphorbia pulcherrima Willd.) [Development of Botrytis cinerea Pers. ex Fr. on leaves of common poinsettia (Euphorbia pulcherrima Willd.)]

The development of Botrytis cinerea was assessed on six cultivars of common poinsettia, differing in the colour of bracts, and being in great demand among buyers of these ornamental plants. Resistance to this pathogen differed in the investigated poinsettias. Cultivar 'Malibu Red' (red bracts) turned out to be most susceptible, while cv. 'Marblestar' (cream-pink) and cv. 'Coco White' (white) - relatively resistant to this fungus. After application of various inoculation methods (leaf discs, cut off leaves, whole plants) the differences in resistance to B. cinerea were confirmed for two extreme cultivars - susceptible ('Malibu Red') and resistant ('Coco White'), which indicated genetic background of this polymorphism. The rate of disease development on poinsettia leaves was affected by the amount of spores used for inoculation (optimum density of 3.5·105 B. cinerea conidia / ml suspension) and the addition of stimulants (0.1 M glucose with 0.05 M KH2PO4), which facilitated germination and infection of the host tissue. The inoculated poinsettia leaves showed high stability of plasma membranes. In the susceptible cultivar, in spite of the development of necrotic spots, a significant increase in the membrane damage index (by 13%) was found only on day 7 of the disease development

Powstawanie wolnych rodników w rozwoju szarej pleśni na liściach poinsecji [The generation of free radicals in the development of grey mould on poinsettia leaves]

Participation of superoxide anion and hydroxyl radical as well as lipoxygenase (LOX) activity and chemiluminescence in the development of grey mould on poinsettia leaves of the cvs.: Coco White – moderately resistant and Malibu Red - susceptible to Botryotinia fuckeliana (B. cinerea) were investigated. In both poinsettia cultivars, the level of superoxide anion radical increased with the disease development. On later dates following inoculation, the content of O2·– in the diseased leaf areas of the susceptible cultivar was 2-fold larger than in grey mould symptom areas of the moderately resistant cultivar. The postinfection generation of a strongly reactive hydroxyl radical was found in the cultivar susceptible to the pathogen. The level of ·–OH in the last hours afier inoculation was 10 fold higher in grey mould spots than in healthy senescing leaves of that cultivar. Tlie activity of LOX exhibited opposite tendencies of changes in the both genotypes examined after the infection. In the first hours after inoculation, the enzyme activity was Low, whereas after 3rd day it significantly increased in diseased leaf areas and in their surroundings. However, in the moderately resistant cultivar the activity of lipoxygenase thoughout the first 3 days of the disease activity was relatively high and then decreased. Poinsettia leaves infected with B. cinerea emitted chemiluminescence. Kinetics and the intensity of ultraweak chemiluminescence depended on the cultivars of poinsettia and on the degree of the disease development. The postinfection increase of chemiluminescence was particularly visible in the zone surrounding diseased areas in the susceptible cultivar